dfd6200a09
A new field 'online' is added to blkg_policy_data to fix following 2 problem: 1) In blkcg_activate_policy(), if pd_alloc_fn() with 'GFP_NOWAIT' failed, 'queue_lock' will be dropped and pd_alloc_fn() will try again without 'GFP_NOWAIT'. In the meantime, remove cgroup can race with it, and pd_offline_fn() will be called without pd_init_fn() and pd_online_fn(). This way null-ptr-deference can be triggered. 2) In order to synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy(), 'list_del_init(&blkg->q_node)' will be delayed to blkg_free_workfn(), hence pd_offline_fn() can be called first in blkg_destroy(), and then blkcg_deactivate_policy() will call it again, we must prevent it. The new field 'online' will be set after pd_online_fn() and will be cleared after pd_offline_fn(), in the meantime pd_offline_fn() will only be called if 'online' is set. Signed-off-by: Yu Kuai <yukuai3@huawei.com> Acked-by: Tejun Heo <tj@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Link: https://lore.kernel.org/r/20230119110350.2287325-3-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.